A number of devices are known in the art to provide rotational alignment or other functions for instruments and the like. U.S. Pat. No. 7,021,592, incorporated herein by reference, includes a flat on a particular face, but it is only used when the device is being stored, not when it is being used. U.S. Pat. No. 6,445,498, incorporated herein by reference, has four knife-edges used to provide rotational alignment of a finder scope. U.S. Pat. No. 6,824,319, incorporated herein by reference, shows two serrated surfaces that interlock with one another. This arrangement eliminates the option of infinite variability of the orientation of the two flanges to one another.
Precision instruments or similar devices may employ a geometry wherein two more or less parallel flanges, connected by a central shaft, are brought together to stop relative movement between the flanges. An example of an application for this would be in a tripod head for a long telephoto lens/camera or a telescope. FIG. 9 illustrates this feature in a tripod head manufactured by Wimberley, Inc. of Winchester Va., assignee of the present application. In FIG. 9, a camera, telescope, or other device 990 (here illustrated as a camera with telephoto lens) may be attached to tripod 990 by means of a tripod head. The tripod head includes a vertical pivot having a rotary axis in the horizontal plane.
The vertical (tilt) pivot includes a movable flange 930 coupled to the camera or telescope 990, and a stationary flange 910 coupled to the tripod head. A knob, nut, or other tightening member 960 may be used to control tension on shaft 920, which pulls movable flange 930 into contact with stationary flange 910 to lock the two flanges together. As can be appreciated by one of ordinary skill in the art, in a situation where a high magnification lens (such as shown) is being used, a user may wish to adjust the vertical angle of the lens to track a target or frame a shot. It would be preferable if a user could move the apparatus in a controlled fashion so as not to overshoot the target or lose a shot.
Note that the term flange is used in the present application for convenience. In the drawings, what is called the stationary flange might alternatively be called a stationary cylindrical housing. The movable flange might be called a movable disk. The term flange captures the fact that each body has a flat surface that is perpendicular to the axis of the shaft or bearing bore, and that the two surfaces mate with one another.
FIG. 1 is a cross-section view of a Prior Art apparatus illustrating the stationary flange 110, movable flange 130, and connecting shaft 120. This type of apparatus may be used to mount a lens, telescope, or other instrument (or other application) at surface 180, for example, on moving flange 130. A nut, knob, or the like may be threaded to shaft 120 (threads omitted for clarity) at point 160 to pull shaft 120 in direction 170 to tighten the assembly. (Other methods, that may or may not require the use of threads on shaft 120, may also be used to pull the shaft in direction 170.)
Note that there is not a tight fit between the bearing surfaces 140A, 140B and shaft 120. The weight of moveable flange 130 and the attached apparatus create a cantilever situation wherein the shaft and flange rotate clockwise until they are constrained by the bearing surfaces 140A and 140B at 190A and 190B. Flanges 110 and 130 may be of the same or different material. A washer, generally of a material different from that of flanges 110 and 130 may be placed between the two flanges 110, 130, at surfaces 150A and 150B. This washer is omitted for clarity in the Figures. FIG. 1 shows the two flanges 110 and 130 far enough apart such that moving flange surface 150B does not touch stationary surface 150A.
FIG. 2 is a cross-section view of a Prior Art apparatus illustrating the two flanges 110, 130 and connecting shaft 120, where the two flanges 110, 130 are just touching at the bottom. This condition occurs as a little tension is placed on the mechanism by tightening the nut or knob (not shown) at the end of shaft 120. A telescope (or other instrument) may be attached to movable flange 130 as illustrated in FIG. 9. An operator may be looking through the telescope. In the condition established in FIG. 1, motion is fairly predictable. As the operator begins to rotate the telescope about a horizontal axis, thus moving the front of the telescope up or down, shaft 110 may first roll up the side of the bearing slightly but will then slip in the bearing and rotate in a way that is consistent with the expectations of the operator. The two components of the mechanism are touching only where shaft 110 contacts bearing surfaces 140A, and 140B at areas 190A and 190B.
In the condition shown in FIG. 2, however, in addition to the contact between the shaft 120 and bearing surfaces 140A, 140B, there is now contact between flange surfaces 150A, 150B. As the movable flange 130 is brought close to the stationary flange 110 by the knob or other tightening mechanism (not shown), contact between the two flanges 110, 130 occurs at a small area (henceforth sometimes called a point) at the bottom of the two flanges 110, 130. In this condition of slight preload wherein the flanges 110, 130 are just touching, the resistance characteristics of the mechanism are quite variable. Initially, the two flanges 110, 130 might be said to stick together at the contact point resisting slipping between one flange and the other. Whereas there is quite a bit of resistance to wholesale slipping between the two flanges 110, 130, there is very little resistance to rotation about this small contact area (actually a lesser sort of slipping).
As a very tiny amount of rotation about the contact point occurs, shaft 120 moves slightly in its housing perpendicular to the plane of the paper of FIG. 2. This initial movement creates very little resistance. When shaft 120 contacts the side of the bearing and can no longer move, the rotation about the contact point ceases and the flanges 110, 130 are forced to rotate past one another. This secondary resistance is much greater because it involves the rubbing of two nearly parallel surfaces contacting at a small area as they move past one another.
Thus, in this state of slight preload, which is typical for the operation of a tripod head, the operator experiences a short period of low resistance to rotation followed by a significant increase in resistance. Each time the operator begins a new adjustment after releasing the lens/camera, he or she experiences the same transition between low resistance and high resistance. This transition results in jerky movement and makes it difficult to accurately aim the lens. Furthermore, when the mechanism is resting in this state of slight preload the connection between the moving flange and the stationary flange is weak with regard to a tiny amount of rotation (the initial low resistance condition). If the mechanism is a tripod head, the connection between the lens/camera and its supporting structure in this condition may be relatively weak. To the extent that the lens/camera is not held solidly, the ability to take sharp, non-blurry, photographs is reduced.